1. Field of the Invention
The present invention relates to spin motors for disk drives; more particularly to low power and low height spin motors.
2. Description of the Related Art
In disk drives or (disk files) for data storage, the disks are rotated so that a transducer which is constrained to move essentially along the radius of the disk can access data at any point on each of the concentric tracks on the disk. In early disk drives, a belt connected the motor to a spindle on which the disks were mounted. Later, spin motors were integrated with the rotating shaft of the disk drive. In a rotating shaft motor, the shaft is supported by bearings mounted to the structural elements of the disk drive and the hub is fixed to the shaft (see, e.g., U.S. Pat. Nos. 4,672,487; 4,692,827; 4,703,374; and 4,739,425).
As spin motors were reduced in size, it became possible to build the spin motor into the hub. In-hub spin motors in which the stator and motor are contained within the hub are disclosed in, for example, U.S. Pat. Nos. 4,739,425 and 4,743,995. Since spin motors for disk drives are conventionally brushless motors, the armature of the motor is referred to as the stator and the magnets are referred to as the rotor. However, in a spin motor where the armature rotates and brushes are used to contact the armature, the armature would be termed the rotor and the magnets would be termed the stator. The diameter of the rotor and stator in an in-hub motor are limited by the inner diameter of the hub which is, in turn, controlled by the inner diameter of the disk or disks mounted on the hub.
The torque created by a motor is related to the product of the radius of the gap between the stator and rotor, the strength of the magnetic field created by the permanent magnets, and the length of the wire in the armature windings in the magnetic field. The torque is also related to the current in the armature windings; torque can be expressed as volts per radian per second, and volts can be expressed in terms of current
In an in-hub spin motor the radius of the gap is limited by the inner diameter of the hub, and the strength of the magnetic field is limited by the characteristics of the permanent magnets. Thus, assuming a fixed magnetic field strength, increasing the torque provided by an in-hub motor, without increasing the current supplied to the motor, requires increasing the length of the armature windings in the magnetic field. The length of the armature windings in the magnetic field can be increased either by providing more windings on the stator or increasing the height of the stator lamination.
In-hub motors are well suited to multiple-disk disk drives where the height of the hub is relatively large. However, in low height disk drives, particularly disk drives intended for use in portable and/or lap-top computers, the height of the disk drive is a critical factor and in-hub motors have not been designed which meet the torque and overall height requirements. In particular, a disk drive having an overall height of approximately one inch or less must utilize a spin motor having a height of less than one inch which creates the torque necessary to provide stable operating speeds and avoids unnecessary spindowns. It has been difficult to construct motors meeting these requirements using an in-hub design.